Related Clues:

• Dots and dashes, e.g.
• ''One if by land, two if by sea,'' e.g.
• One if by land, two if by sea, e.g.
• Something cracked
• Programmer's creation
• It's broken after some thought
• Spy-school subject
• UPC part
• Cracker's target
• It may be cracked by a spy
• Programmer's concern
• It can't be understood until it's broken
• "The Da Vinci ___"
• Bed intruders?
• 0, or a code